In the prior art, the drill chuck is provided with a drill body, a clamping jaw, a nut, and by rotating the nut to move the clamping jaw forward or backward, the drilling tool is clamped or loosened by the drill chuck. The self-locking structure in the drill chuck is designed to prevent the drill chuck from being dislodged by the reaction force applied during operation. Usually the parts with leaf spring are coordinated with the teeth on the drill body. The drill chuck is a structure maintaining self-locking state or non-self-locking state, which is formed by matching between the convex on the leaf spring and groove on the inner wall of engineering plastics of the rotating sleeve; under a high-speed rotation state, its retention force is sometimes inadequate, to make self-locking failure.